(a) Field of the Invention
The present invention relates to a microcontact printing method, and more specifically, to a microcontact printing method using a nanoimprinted nanostructure to transfer a pattern with a size of several tens of nanometers.
(b) Description of Related Art
Nanoimprint lithography technology is a technology for pressing a surface of a polymer resist coated on a substrate with a stamp having an imprinted nanostructure thereon to transfer the nanostructure.
In the nanoimprint process initially developed by Prof. Chou at Princeton Univ. in 1996, a base sheet coated with a polymethylmethacrylate (PMMA) resist is pressed with a stamp having a nano-sized embossed structure fabricated by an electronic beam lithography process at a high temperature, and is then separated in a cooling process. Accordingly, a negative pattern of the nanostructure embossed on the stamp is imprinted on the resist, and a residual resist that remains at a pressed portion of the resist surface is completely removed through anisotropic etching.
After that, a laser-assisted direct imprint (LADI) method, one of the nanoimprint methods, was developed. The LADI method uses a single 20 ns excimer laser having a wavelength of 308 nm to instantaneously melt a silicon wafer or a resist coated on the silicon wafer. Similarly, nanosecond laser-assisted nanoimprint lithography (LA-NIL) applied to polymer was developed. The LA-NIL imprints the nanostructure having a line width of 100 nm and a depth of 90 nm on the polymer-based resist.
In addition, Prof. Sreenivasan et al. at the University of Texas at Austin proposed a step & flash imprint lithography (SFIL) process in 1999. Through this process, a nanostructure can be fabricated at room temperature by using a UV light curing material. In the SFIL process, the nanostructure is imprinted by using a UV transmissive material such as quartz or Pyrex glass as a stamp, and is cured by UV light.
Further, a microcontact printing method, which is a typical soft lithography process, includes steps of fabricating a polydimethylsiloxane (PDMS) stamp; giving functionality to patterns to transfer the patterns to the base; and obtaining the same pattern as a mold through etching and deposition processes.
In the microcontact printing, an elastomer stamp having a fabricated pattern thereon is duplicated from a master. In addition, the elastomer stamp is dipped into a monolayer-forming ink. Here, a wet ink or a contact ink is used. The dipped stamp is used to print the pattern, and the printed pattern protects a metal base layer during the subsequent etching process.
However, With the microcontact printing process, it is difficult to have an independent processing condition due to several problems in processing. That is, it is necessary to experimentally verify the process of applying a high resolution (less than 20 nm) pattern using the elastomer.
For example, distortion or deformation related to the elastomer material should be avoided. In the current patterning molding process, problems include: a paring problem in that gravity, adhesive strength, and capillary forces are exerted on the elastomer material to collapse a shape thereof or incur defects; a sagging problem in that the elastomer material sags when a ratio of a patterned portion to the remaining non-patterned portion is low; and a shrinking problem in that an accurate record cannot be made due to a flexible PIMS.
Furthermore, the pattern transfer should have accurate reproducibility, and the quality of formed patterns and structures should be improved. However, the microcontact printing process does not yet meet the requirement of a fine line pattern for a complicated electronic apparatus.
The conventional microcontact printing process can implement a micro pattern of up to 300 nm due to the characteristics of polymer, while it is almost impossible to implement the micro pattern of less than 100 nm due to poor resolution and excessive defects.
In addition, when fabricated in a multi-layered structure, the conventional microcontact printing process has a problem in that misalignment may occur due to deformation of the pattern and distortion of the structure during a deposition process.